Direct formic acid fuel cells are a sustainable alternative to batteries in portable electronics due to their high efficiency, 24/7 operating capabilities, and instantaneous refueling times. However, the anode catalyst layer’s small pore size (~20 nm) between catalyst agglomerates causes two-phase mass transport limitations that plague the fuel cell performance. Thus, to improve cell performance, the two-phase flow of liquid reactant (formic acid, HCOOH) and gaseous product (carbon dioxide, CO₂) must be optimized. To optimize the two-phase flow, a magnesium oxide pore-forming agent is added into the anode catalyst ink and subsequently removed after the catalyst layer fabrication to increase the porosity of the catalyst layer.

In this groups prior work, Bauskar et al. incorporated and removed pore-former (lithium carbonate, LiCO₃) to form ~10 μm pores within the anode catalyst layer. [1] Performance was optimized for anode catalyst layer with pores formed from 17.5 wt% LiCO₃. However, the size of the pore-former increased catalyst agglomerate separation and reduced the connected electrochemical surface area resulting in reduced formic acid electrooxidation charge transfer activity.

Previous work to incorporate smaller pores via a smaller pore-former (magnesium oxide, MgO, ~50 nm) showed that, at 25 wt% pore-former, the electrochemical surface area and cell performance increased by 293% and 86%, respectfully, compared to an anode catalyst layer with no pore-former. [2] The present study explores a higher range of varying pore-former wt% while also investigating the effects of sonication of the catalyst ink via in-situ catalyst layer characterization, scanning electron microscopy, and catalyst ink rheology.

1. Bauskar, A.S. and Rice, C.A., Impact of Anode Catalyst Layer Porosity on the Performance of a Direct Formic Acid Fuel cell. Electrochimica Acta 2012, 62, 36-41.
2. Lam, S., Bixby, M.M., and Rice, C.A., Optimization of Mass Transport within Direct Formic Acid Fuel Cell Catalyst Layer via Pore Formers. ECS Trans 2020, 98, 355.